WO2019126316A1

WO2019126316A1 - Hydrodehalogenation of polyhalogenated aromatics catalyzed by nickel/palladium nanoparticles supported on nitrogen-doped graphene

Info

Publication number: WO2019126316A1
Application number: PCT/US2018/066489
Authority: WO
Inventors: Xuefeng Guo; Chao YU; Shouheng Sun; Christopher T. Seto; Zhouyang YIN
Original assignee: Brown University
Priority date: 2017-12-19
Filing date: 2018-12-19
Publication date: 2019-06-27

Abstract

The invention provides an assembly of nickel/palladium nanoparticles on nitrogen-doped graphene as an efficient catalyst for near quantitative degradation of various halogenated aromatics, including polyhalogenated organic pollutants, under green chemistry conditions.

Description

TITLE OF THE INVENTION

[0001] HYDRODEHALOGENATION OF POLYHALOGENATED AROMATICS

CATALYZED BY NICKEL/PALLADIUM NANOPARTICLES SUPPORTED ON

NITROGEN-DOPED GRAPHENE

FIELD OF THE INVENTION

[0002] This relates generally to catalysts characterized by their form or physical properties, comprising metals or metal oxides or hydroxides, including the metal nickel, methods of making a catalyst, and to hydrogen production from non-carbon containing sources by decomposition of partly inorganic compounds.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] This invention was made with government support under grant W91 1 NF-15-1- 0147 awarded by the U.S. Army. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0004] The activation of halogenated arene (CArX) (X = halogen) bonds to achieve full conversion to unhalogenated arene (CArH) is the key step in the degradation of polyhalogenated aromatics (PHAs). Conventional methods to accomplish this degradation rely on hydrodehalogenation reactions in the presence of a catalyst with either isopropanol or pressurized H₂ as the hydrogen source. Catalysts designed for this degradation are based on transition metal complexes of Pd, Rh, Ni, Co or Fe. For transition metal complexes of Pd, see Pyo et al., Tetrahedron Lett. 54, 5207-5210 (2013); Iranpoor ef a/., J. Organomet. Chem. 695, 887-890 (2010), and Navarro et a!., J. Org. Chem. 71 , 685-692 (2006). For transition metal complexes of Rh, see, You et al., J. Org. Chem. 82, 1340-1346 (2017); Lazaro et al., ChemSusChem 8, 495-503 (2015) and Fujita et al., Chem. Commun. 2964-2965 (2002). For transition metal complexes of Ni, see, Mochizuki & Suzuki, Inorg. Chem. Commun., 14, 902-905 (201 1). For transition metal complexes of Co, see Chan et al., Tetrahedron Lett. 56, 2728-2731 (2015). For transition metal complexes of Fe, see, Czaplik et al., Chem. Commun. 46, 6350-6352 (2010) and Guo et al., Chem. Lett. 33, 1356- 1357 (2004)). Transition metal complexes are normally used under homogeneous reaction conditions. However, these catalysts often require complexation by phosphine ligands that are neither stable under the reaction conditions, nor environmentally friendly.

[0005] Growing concerns over the continued accumulation of polyhalogenated aromatics in the environment have motived the development of more efficient catalysts to reduce halogenated arene (CArX) bonds under mild and environmentally-friendly reaction conditions. One approach by bio-remediation. Several species of microalgae and cyanobacteria show potential for degrading chlorinated organic pollutants such as dichlorophenols and polychlorinated biphenyls (PCBs). However, extended reaction times lasting from weeks to months are needed to degrade low concentrations of pollutants in soil. In addition, such biodegradation only leads to partial dechlorination of polyhalogenated aromatics.

[0006] A different approach uses nanostructured composites of Fe(0) and Pd(0). See, Kopinke, Envir. Sci. Techno!., 46, 1 1467-1 1468 (2012) and Y. Zhuang et a!., Envir. Sci. Technol., 45, 4896- 4903 (201 1). Fe is used to reduce water to provide H2 for the subsequent hydrogenation reaction, while Pd catalyzes the hydrochlorination of chlorinated arene (CArCI) bonds. However, Fe(0) is oxidized in this process and must be regenerated by a stronger reducing agent, such as sodium borohydride, for the catalysis to proceed. In addition, the composite catalyst does not have a high enough efficiency to dechlorinate high concentrations of polyhalogenated aromatics.

[0007] In the presence of a hydrogen source, palladium (Pd)-based nanoparticles can convert CArX to CArH. Conventional sources of hydrogen for the reaction come from either pressurized hydrogen gas or the decomposition of an alcohol at high temperature. Goswami et al., ACS Appl. Mater. Inter., 9, 2815-2824 (2017); Rong et a!., ACS Catal., 3, 1560-1563 (2013); and Shiraishi et al., Chem. Commun., 47, 7863-7865 (201 1).

Palladium-based nanoparticles can also catalyze the dehydrogenation of ammonia borane in water to generate hydrogen gas, which can subsequently be used to reduce nitro compounds to amines. Yu et at, Chem. Mater., 29, 1413-1418 (2017); Zhan et at, ACS Catal., 6, 6892-6905 (2016); and Goksu et al., ACS Catal., 4, 1777-1782 (2014). This strategy has been further extended in a multicomponent coupling reaction to synthesize quinazolines. Yu et al., J. Am. Chem. Soc., 139, 5712- 5715 (2017) and Yu et al., Angew. Chem.).

[0008] There remains a need in the catalytic art for better nickel/palladium

(Nickel/palladium) catalysts to reduce halogenated aromatics in the environment to their corresponding aromatics.

SUMMARY OF THE INVENTION

[0009] The invention provides an efficient nickel/palladium (NiPd) catalyst for the reduction of halogenated (e.g., chlorinated or brominated) aromatics to the

corresponding aromatics in near quantitative yield in 10% aqueous isopropanol solvent at or below 50°C. [0010] In a first embodiment, the invention provides a catalytic material for catalyzing a chemical change, conversion or synthesis, the change, conversion or synthesis being the reduction of halogenated aromatics to their corresponding aromatics. The catalytic material of the invention comprises nickel/palladium (NiPd) alloy nanoparticles (NP) supported (or assembled) on nitrogen-doped graphene (NG). The nickel/palladium alloy nanoparticles supported on nitrogen-doped graphene effectively catalyze a tandem reaction. The first reaction is the reduction of halogenated aromatics to their

corresponding aromatics. The second reaction is the oxygenation of a hydrogen source. Because the hydrodechlorination reaction generates hydrochloride acid, nitrogen-doped graphene is used as the support for the nickel/palladium nanoparticles. The catalytic material of the invention does not require complexation by phosphine ligands, which are neither stable under usual reaction conditions nor environmentally friendly.

[0011] In a fourth embodiment, the invention provides a method of preparing nitrogen- doped graphene. A shown in FIG 1 A, the inventors tested the assembly conditions and found that a 1 :1 w/w mixture of NPs/NG results in a well-dispersed layer of nanoparticles on the nitrogen-doped graphene surface, forming a monolayer assembly on each nitrogen-doped graphene sheet.

[0012] In a second embodiment, the hydrogen source is ammonia borane (AB, H3NBH3). Ammonia borane has recently become a popular choice as a hydrogen source for the reduction process due to its high volume/mass hydrogen density, its nontoxicity and its high-solubility in water.

[0013] In a third embodiment, the catalytic material of the invention comprises nickel/palladium nanoparticles between 2 nm in length and 4 nm in length. In a fourth embodiment, the nickel/palladium nanoparticles are about 3 nm in length. The inventors initially prepared metal/palladium nanoparticles of size 3-4 nm.

[0014] In a fifth embodiment, the catalytic material of the invention can catalyze not only the reduction of monohalogenated aromatics, but also the reduction of polyhalogenated aromatics, including dioxin, polychlorinated biphenyls (PCB), polybrominated diphenyl ethers (PBDEs) and the components of the defoliant Agent Orange.

[0015] The catalytic material of the invention can be recycled through several sequential hydrodehalogenation reactions. In a sixth embodiment, the catalytic material of the invention is recoverable and reusable at least five times without loss of catalytic activity.

In a seventh embodiment, the catalytic material of the invention is recovered and reused at least five times without loss of catalytic activity.

[0016] In an eighth embodiment, the catalytic material of the invention is used for environmental remediation. In a ninth embodiment, the invention provides a method of environmental remediation using the catalytic material of the invention to convert (or degrade) halogenated arene (CArX) to unhalogenated arene (CArH). The method comprises the steps of contacting the catalytic material of the invention with halogenated arene in the environment, so that the catalysis results in the dehalogenation of environmental unhalogenated arene compounds

[0017] In a tenth embodiment, the catalytic material of the invention is used to synthesize a pharmaceutical compound or a pharmaceutical intermediate. In an eleventh embodiment, the invention provides a method of synthesis using the catalytic material of the invention to convert a compound to a pharmaceutical compound or a pharmaceutical intermediate.

[0018] In a twelfth embodiment, the invention provides catalytic material comprising nanoparticle catalysts for ammonia borane-initiated chlorinated arene (CArCI) conversion to unchlorinated arene (CArH).

[0019] In a thirteenth embodiment, the invention provides nanoparticles that have a Ni₃oPd₇o, N oPdeo or other palladium-rich polycrystalline structure, wherein nickel content is no more than 50%. In a fourteenth embodiment, the catalytic material of the invention comprises a nickel/palladium alloy on nitrogen-doped graphene of form Ni₃oPd₇o/NG. After testing the ammonia borane-initiated transfer hydrogenation and

hydrodechlorination of chlorobenzene and dichlorobenzene, the inventors found that Ni₃₀Pd₇o/NG is more active than Ni₃₀Pd₇o/C and Ni₃₀Pd₇o/G. As shown in FIG 1 B-1 D, the inventors further synthesized and tested Ni₅₄Pd₄₆/NG, Ni_6iPd₃₃/NG and Pd/NG, and found Ni₃₀Pd₇o/NG to be the most efficient catalyst for the reaction. FIG. 3 shows the optimization of the Ni₃₀Pd₇o/NG-catalyzed hydrodechlorination of dichlorobenzene. As shown in FIG. 6, the inventors deposited these nanoparticles onto common carbon (C) or graphene (G) supports and studied the catalysis by nanoparticles in the ammonia borane-initiated hydrodechlorination of chlorobenzene in a solution of 10% aqueous isopropanol. Nickel/palladium nanoparticles are more effective than either

copper/palladium or iron/palladium.

[0020] In a fourteenth embodiment, the invention provides a method of preparing nitrogen-doped graphene was using pyridine-N rich, which can provide necessary anchoring sites for the Nickel/palladium nanoparticles and enrich arene to promote the hydrodechlorination reaction. Yang et al., Sci. Adv. 2, (2016); Shui et al., Sci. Adv. 1 , (2015). The inventors then assembled 3 nm Ni₃₀Pdi₀ nanoparticles on nitrogen-doped graphene by mixing and sonicating a hexane dispersion of nanoparticles and nitrogen- doped graphene.

[0021] In a fourth embodiment, the invention provides nanoparticles where the activity is tuned by one or more steps selected from the group of controlling molar ratio of nickel and palladium salts in a solution phase co-reduction particle-producing reaction;

controlling temperature of solution phase co-reduction of nickel and palladium; or both.

[0022] In a fourth embodiment, the invention provides a process for making a nanoparticle catalyst useful in solution phase synthesis of organic amines, the process comprising the steps of forming polycrystalline nickel/palladium alloy nanoparticles, and assembling the nanoparticles on a carbon support.

[0023] In a fourth embodiment, the invention provides a catalyst made by the process, wherein the carbon support is nitrogen-doped graphene and the nanoparticles are effective to catalyze tandem dehydrogenation and hydrogenation reactions in liquid phase using ammonia borane as a source or hydrogen to produce primary amines.

[0024] In a fourth embodiment, the invention provides a method of environmental remediation, comprising the steps of contacting a catalytic material comprising palladium-rich nickel palladium (Nickel/palladium) alloy nanoparticles supported on nitrogen-doped graphene, which catalytic material is effective to catalyze a tandem reaction that (1) converts a halogenated arene compound to an unhalogenated arene compound; and (2) hydrogenates a second nitrogen-containing feedstock or group to primary amine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a set of transmission electron microscopy (TEM) images of

nickel/palladium nanoparticles (NPs) on nitrogen-doped graphene (NG). (A) TEM image of 3.0±0.1 nm Nh0Pd10/NG. (B) TEM image of 3.4±0.3 nm Nis4Pd46/NG. (C) TEM image of 3.8±0.2 nm Ni_6iPd₃3/NG. (D) TEM image of 4.0±0.2 nm Pd/NG. These NiPd/NG samples were prepared by mixing hexane dispersions of nickel/palladium nanoparticles and nitrogen-doped graphene in 1 :1 mass ratios. Each transmission electron microscopy sample was prepared by adding a drop of hexane dispersion of NiPd/NG on an amorphous carbon-coated copper grid followed by hexane evaporation under ambient conditions.

[0026] FIG. 2 is a set of charts showing time-dependent hydrodechlorination of chlorobenzene and dichlorobenzene catalyzed by Ni₃oPdio/NG catalyst. (A)

Dechlorination of chlorobenzene. Reaction conditions: chlorobenzene (1 mmol), ammonia borane (2 mmol), 10% aqueous isopropanol (3.0 mL) and NiPd/NG (3 mol%) at 40°C. (B) Dechlorination of dichlorobenzene. Reaction conditions: dichlorobenzene (1 mmol), ammonia borane (6 mmol), 10% aqueous isopropanol (3.0 mL) and NiPd/NG (3 mol%) at 50 °C.

[0027] FIG. 3 is a table showing hydrodehalogenation of dichlorobenzene catalyzed by Pd-based catalysts on different carbon supports. Reaction conditions: dichlorobenzene (1 mmol), ammonia borane (6 mmol), 10% aqueous isopropanol (3.0 mL) and catalyst (3 mol %) for 5 hours at 50°C. (b) Yields were determined by GC-MS.

[0028] FIG. 4 is a table showing the hydrodehalogenation of mono-halogen substituted compounds. Reaction conditions: aryl halides (1 mmol), ammonia borane (2 mmol), 10% aqueous isopropanol (3.0 mL) and NiPd/NG (3 mol%) for 3 hours at 40°C. (b) Isolated yield except where noted otherwise (c) Yield determined by GC-MS.

[0029] FIG. 5 is a set of transmission electron microscopy (TEM) images of (A) 3±0.1 nm NhoPdio, (B) 3±0.2 nm C0_2iPd₇₃, and (C) 3±0.4 nm Fe₃2Pd65.

[0030] FIG. 6 is a set of transmission electron microscopy (TEM) images of (A)

NboPdyo/C, (B) NboPdyo/G, (C) C0_2iPd₇₃/C, (D) Co_2iPd₇₃/G, (E) Fe₃₂Pd₆₅/C, and (F) Fe₃₂Pd65/G.

[0031] FIG. 7 is a table showing the hydrodehalogenation of multi-halogen substrates. Reaction conditions: organic halides (1 mmol), ammonia borane (3.0 equiv. with respect to halogen atoms), 10% aqueous isopropanol (3.0 mL) and NiPd/NG (3 mol%) at 50 °C. (b) Isolated yield except where noted (c) Yield determined by GC-MS. (d) 0.003 mmol (1 mg) of dioxin was used in the reaction (e) Reaction was run for 12 hours (f) 0.04 mmol of decachlorobiphenyl was used in the reaction.

[0032] FIG. 8 is a table showing the recycling of NiPd/NG for hydrodehalogenation of dichlorobenzene. Reaction conditions: dichlorobenzene (1 mmol), ammonia borane (6 mmol), 10% aqueous isopropanol (3.0 mL) and NiPd/NG (3 mol%) for 5 hours at 50°C. Yields were determined by GC-MS.

[0033] FIG. 9 is a transmission electron microscopy (TEM) image of

Nickel/palladium/NG after 5th reaction recycling.

INDUSTRIAL APPLICABILITY

[0034] Polyhalogenated aromatics (PHAs), such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), are a class of persistent organic pollutants that adversely affect human health. The CAr-CI (97.1 kcal/mol) and (CAr-Br 84.0 kcal/mol) bonds are stable. Blanksby & Ellison, Accounts Chem. Res. 36, 255-263 (2003)) Thus, polyhalogenated aromatics are extremely difficult to degrade in the natural environment, and can accumulate and pass from one organism to another through the food chain. Polyhalogenated aromatics are easily spread by wind and water, so they can cause serious long-term detrimental effects to humans and wildlife even far from where they are used and released into the environment. Despite recent restrictions imposed on the use and production of polyhalogenated aromatics, environmental concentrations of polyhalogenated aromatics remain high, especially in areas where pesticides, transformer oil, or fire-retardant materials have been heavily used. A recent survey of polychlorinated biphenyl concentrations revealed that more than 21 ,000 tons of polychlorinated biphenyls exist in the surface soil globally. Dalla Valle et ai, Environ. Pollut., 134, 153-164 (2005). The defoliant Agent Orange is comprised of a 1 : 1 mixture of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid. It also contains 2,3,7,8-tetrachlorodibenzo-p-dioxin as a significant contaminant that is generated during the manufacture of the defoliant. Even after 30 years, concentrations as high as 1000 mg/kg of dioxin can still be found in selected soil and sediment samples from affected areas of Vietnam. Banout et a!., J. Environ. Public Health, 2014, 528965 (2014).

Therefore, it is extremely important to develop new technologies to degrade

polyhalogenated aromatics to eliminate their adverse impact on the environment, and in particular in areas that contain high concentrations of polyhalogenated aromatic pollutants.

[0035] The invention provides a Ni₃oPd7o/nitrogen-doped graphene (NG) catalyst that hydrodehalogenates halogenated aromatics under mild reaction conditions. The catalyst reduces monochloroarenes or dichloroarenes to the corresponding dehalogenated arenes in >90% yield in 10% aqueous isopropanol solvent at or below 50°C within 5 hours. Tests on a variety of substrates containing hydroxyl, amine, amide and carboxylic acid functional groups show that the catalyst is selective for reduction of C-CI and C-Br bonds. In addition, this catalyst completely hydrodehalogenates high concentration solutions of dioxin, polychlorinated biphenyls (PCBs), chloroaromatic constituents of the defoliant Agent Orange, and polybrominated diphenyl ethers (PBDEs) in 12 hours. The catalyst is reusable and shows no morphological or compositional changes after five reaction cycles. This methodology offers a powerful, low-cost and safe technology for the degradation of polyhalogenated aromatics, preventing proliferation of these toxins in the environment from causing serious health issues.

[0036] The NiPd/NG catalyst of the invention shows superior performance for the hydrodehalogenation of polyhalogenated aromatics under mild and environmentally friendly reaction conditions. Dehalogenation reactions often require strong bases, strong reducing agents and harsh reaction conditions including high temperatures, but the NiPd /NG system of the invention uses ammonia borane as the hydrogen source and base, and an aqueous solvent system. The reaction is compatible with a variety of functional groups including hydroxyl groups, amines, amides and carboxylic acids. Under these mild conditions, the NiPd/NG catalyst promotes the complete dehalogenation of several severe environmental contaminants including the components of agent orange, dioxins, polychlorinated biphenyls and polybrominated diphenyl ethers, which are extremely difficult to decontaminate using conventional methods. This concept of exploiting nanoparticles for Green Chemistry applications may provide a promising avenue for the rational design and assembly of nanostructured catalysts for solving long-standing problems in environmental chemistry.

BEST MODE FOR CARRYING OUT THE INVENTION

Definitions

[0037]“CArH” indicates an arene (aryl hydrocarbon) group attached to another carbon.

[0038]“CArX” indicates a halogenated arene (aryl hydrocarbon) group attached to another carbon.

[0039]“Nanoparticles” are particles between 1 and 100 nanometers (nm) in size with a surrounding interfacial layer. The interfacial layer is an integral part of nanoscale matter, fundamentally affecting all of its properties. Metal nanoparticles can have

electromagnetic properties different from the bulk metal. This can be caused by surface effects due to the high surface area to volume ratio. As used in this patent application, metal/palladium nanoparticles are less than 10 nm in size. U.S. Pat. Pub. US

2016/0279619 A1 (Sun et al.) describes how nickel/palladium nanoparticle size and composition can be controlled by the temperature at which the metal precursors are injected into the reaction.

[0040]“About” as the term is used to describe nanoparticle size means that most of the nanoparticles are ±0.1 nm of the specified nanoparticle size.

Materials and Methods

[0041] Materials. The inventors carried out the nanoparticle synthesis using standard airless procedures and commercially available reagents. The inventors used all reagents as received. The main chemicals including borane-fe/f-butylamine complex (BBA, 97%), palladium(ll) acetylacetonate (Pd(acac)2, 99%), nickel(ll) acetylacetonate (Ni(acac)2, 95%), copper(ll) acetylacetonate (Cu(acac)2, 98%), cobalt(lll) acetylacetonate

(Co(acac)3, 99%) and iron(lll) acetylacetonate (Fe(acac)3, 99%), are commercially available from Strem Chemicals, Newburyport, MA, USA. Oleylamine (OAm) (>70%), 1- octadecene (ODE, 90%), ammonia borane (orborane-ammonia complex, NH₃BH₃, 90%), and aryl halides used in the dehalogenation reactions are commercially available from Sigma-Aldrich, St. Louis, MO, USA.

[0042] Synthesis of Pd nanoparticles. Under a gentle flow of N₂, 200 mg of BBA, 6 mL of OAm, and 4 mL of ODE were mixed, stirred by a magnetic bar and heated to 120°C for 10 min. The solution was kept at this temperature for another 30 min before it was cooled to 100°C. In a separate vial, 4.0 mmol of Pd(acac)2 was dissolved in 3 mL of 1- octadecene and the solution was added via a syringe quickly into the 100°C solution.

The mixed solution was stirred at 100°C for 1 hour and cooled to room temperature.

Then ethanol was added, and the nanoparticle product was separated by centrifugation at 9000 rpm for 15 min. Next, the nanoparticles were washed with hexane/ethanol (v/v= 1 :15) by centrifugation at 9000 rpm for 20 min. The obtained powder was dispersed in hexane for further use.

[0043] U.S. Pat. Pub. US 2016/0279619 A1 (Sun et al.) describes a synthesis of nickel/palladium nanoparticles that can be adapted by one of ordinary skill in the catalytic arts for the synthesis of the catalyst of the invention. Sun et al. prepared by

nickel/palladium nanoparticles by the co-reduction of nickel- and palladium-salt precursors by borane-fe/f-butylamine (BBA) in oleylamine. The nickel/palladium nanoparticles so produced were active not only for ammonia borane dehydrogenation, but also for the hydrogenation of R— N0₂ and/or R— CN to RNH₂. Further, when the nickel/palladium nanoparticles were deposited on graphene (G), they became a highly efficient catalyst for tandem ammonia borane dehydrogenation and hydrogenation reactions in aqueous solution at room temperature. Sun et al., disclose an improved method and materials for catalytic production of primary amines, including a facile route to monodisperse 3.4 nm nickel/palladium alloy nanoparticles which, when deposited on graphene (G) support using solution-phase self-assembly, were demonstrated to be efficient in catalyzing the tandem reaction of dehydrogenation of ammonia borane and hydrogenation of R— N0₂ or R— CN to produce primary amines R— NH₂. However, the nanoparticles actually produced by Sun et al. did not - among other things - effectively catalyze the conversions of halogenated arenes to unhalogenated arene in an environmentally useful manner. The Sun et al. catalytic material was not deposited on nitrogen-doped graphene.

[0044] Metin et al., Nano Research, 6(1), 10-18 (2013) discloses several methods of making nickel/palladium nanoparticles that can be adapted by one of ordinary skill in the catalytic art to make the nickel/palladium nanoparticles of the invention. Metin et al. made graphene-supported nickel/palladium alloy nanoparticle catalysts for Suzuki- Miyaura cross-coupling reactions. The Metin et al. nanoparticles have a size distribution with a mean particle size of 10 nm, and include larger nanoparticles that are 10-, 15-, 20- or 50 nm in diameter. The Metin et al. nanoparticles are fabricated as bimetallic coreshell nanoparticles made by sequential reduction of the two metal salts, so that one metal is reduced and forms nanoparticles thereof: which constitute cores, and following which the second metal is then deposited as a shell surrounding the core, rather than solution alloy nickel/palladium nanoparticles. However, Metin et al., disclose a method for making a single sheet of graphene oxide synthesized from natural graphite powder by exfoliation of graphene oxide under ultrasonication in dimethylformamide, method for the characterization of the nickel/palladium nanoparticles, and other methods. [0045] Zhang et al., New J. Chem. 36, 2533-2540 (2012) disclosed a uniform dispersion of Ni/Pd nanoparticle catalysts supported on graphene oxide with average size 4 nm.

[0046] Synthesis of Nί₃oR ₇o alloy nanoparticles. The synthesis was similar to that described above for the synthesis of Pd nanoparticles, except that in a separate vial, 2.0 mmol of Pd(acac)₂ and 3.0 mmol of Ni(acac)₂ were dissolved in 3 mL of 1-octadecene.

The synthesis was similar to that

described above for the synthesis of Pd nanoparticles, except that in a separate vial, 1.5 mmol of Pd(acac)2 and 3.5 mmol of Co(acac)3 were dissolved in 3 mL of 1-octadecene.

[0048] Synthesis of Cu_3iPdeg alloy nanoparticles. The synthesis was similar to that described above for the synthesis of Pd nanoparticles, except that in a separate vial, 2.2 mmol of Pd(acac)₂ and 2.8 mmol of Cu(acac)₂ were dissolved in 3 mL of 1-octadecene.

[0049] Synthesis of Fe^Pd^ alloy nanoparticles. The synthesis was similar to that described above for the synthesis of Pd nanoparticles, except that in a separate vial, 1.3 mmol of Pd(acac)₂ and 3.7 mmol of Fe(acac)₃ were dissolved in 3 mL of 1-octadecene.

[0050] Synthesis of Ni^Pd^ alloy nanoparticles. The synthesis was similar to that described above for the synthesis of Pd nanoparticles, except that in a separate vial, 2.0 mmol of Pd(acac)₂ and 4.0 mmol of Ni(acac)₂ were dissolved in 3 mL of 1-octadecene.

[0051] Synthesis of NimPdaa alloy nanoparticles. The synthesis was similar to that described above for the synthesis of Pd nanoparticles, except that in a separate vial, 1.5 mmol of Pd(acac)₂ and 4.0 mmol of Ni(acac)₂ were dissolved in 3 mL of 1-octadecene.

[0052] Synthesis of nitrogen-doped graphene (NG). 2.0 g melamine and 0.4 g singlelayered graphene oxide were mixed in 400 mL deionized water and stirred at room temperature for 48 hours. Water was then evaporated at 60°C. The resulting solid product was first annealed at 350°C for 0.5 hour and then at 900°C for 1 hour under a N₂ atmosphere. After cooled to room temperature, the powder was ready for further use.

[0053] Assembly of nanoparticles on nitrogen-doped graphene. Ten mg of the nanoparticles were dispersed in 5 .0 mL of hexane and the dispersion was added drop- wise into a suspension of 10.0 mg of nitrogen-doped graphene in ethanol (60 mL) in an ultrasonic environment. After the addition of the nanoparticle dispersion, the

ethanol/hexane mixture was sonicated for 2 hours to ensure complete adsorption of the nanoparticles onto nitrogen-doped graphene. [0054] Synthesis of PCB substrates. Chloroaryl bromide (5 mmol), chloroaryl boronic acid (5 mmol), K3PO4 (10 mmol), Pd(OAc)2 (10 mg) and 20 mL of DMF/H2O (1/1) were added to a round bottom flask. The reaction mixture was stirred at room temperature for 24 hours. The aqueous phase was extracted with ethyl acetate (3 x 20 mL), the combined organic extracts were washed with water (3 x 50 mL), dried over Na₂S0₄ and the solvents were removed in vacuo. The crude product was purified by flash column chromatography.

[0055] General procedure for the hvdrodehalogenation reactions. The aryl halide (1 mmol), NPs/NG (10 mg, 3 mol %), NH3BH3 (3 mmol) and 10% aqueous isopropanol (3 mL) were stirred in a 10 mL sealed tube at 50°C for 5 hours. After the reaction was complete, the catalyst was filtered and the mixture was extracted with ethyl acetate. The organic phase was evaporated under vacuum and purified by flash column

chromatography (hexane/ethyl acetate= 8:1) to give the final product.

[0056] Catalyst reuse. After the reaction was complete, the nanoparticles/NG catalyst was filtered from the reaction mixture and washed with water and isopropanol. The catalyst was then dried, weighed, and used directly for the next round of reaction.

[0057] Characterization of the synthesized nanoparticle catalyst materials. Samples for transmission electron microscopy (TEM) were prepared by depositing a single drop of diluted NP dispersion/suspension on amorphous-carbon-coated copper grids. Images were obtained using a JEOL 2010 TEM (200 kV). The compositions of the nanoparticles and the molar ratio of NPs/NG were measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0058] For inductively coupled plasma-atomic emission spectroscopy analyses, the dried nanoparticles were dissolved in warm aqua regia (~70°C, 30 min) to ensure the complete dissolution of metal into the acid. The solution was then diluted with 2% HN0₃ solution. The measurements were carried out on a JY2000 Ultrace ICP-AES equipped with a JY- AS 421 auto sampler and 2400 g/mm holographic grating.

[0059] Thin-layer chromatography (TLC) analysis was done using silica gel TLC plates with 60 F254 indicators, glass backed.

[0060] The analyses of reaction products were carried out by gas chromatography-mass spectroscopy (GC-MS) using an Agilent 6890 GC coupled to a 5973 mass spectrometer detector with a DB-5 (Agilent) fused silica capillary column (L x I.D. 30 m x 0.25 mm, df 0.25 pm) and helium as carrier gas. The gas chromatograph was temperature programmed from 65°C (3 min initial time) to 300°C at 6°C/min (isothermal for 20 min final time). The mass spectrometer was operated in the electron impact mode at 70 eV ionization energy. Mass spectrometric data were acquired and processed using the GC- MS data system (Agilent Chemstation), and compounds were identified by gas chromatographic retention index and mass spectrum comparison with authentic standards, literature and library data, and unknown compounds were characterized by interpretation of the fragmentation pattern of their mass spectra. NMR spectra were recorded using a Bruker Avance III Ultra-Shield Spectrometer (400 MHz for ¹H, 100 MHz for ¹³C) at 296 K. Chemical shifts are reported in ppm relative to the residual solvent signal (CDCh: 7.26 ppm (¹H), 77.16 ppm (¹³C) ), coupling constants (J) are reported in Hz.

[0061] U.S. Pat. Pub. US 2016/0279619 A1 (Sun et al.) describes methods of the characterization of nickel/palladium nanoparticles that one of ordinary skill in the catalytic arts can adapt to characterize the catalyst of the invention. See also, Goksu et al., ACS Catai, 4(6), 1777-1782 (2014). Sun et al. prepared samples for transmission electron microscopy by depositing a single drop of the diluted NP dispersion in hexane amorphous carbon coated copper grids. Images were obtained on a Philips CM20 at 200 kV. High resolution TEM images were obtained on a JEOL 21 OOF with an accelerating voltage of 200 kV. X-ray diffraction patterns were collected on a Bruker AXS D8- Advanced diffractometer with Cu Ka radiation (l=1.5418 A).

[0062] Sun et al. carried out inductively coupled plasma elemental analysis

measurements a JY2000 Ultrace ICP Atomic Emission Spectrometer equipped with a JY AS 421 autosampler and 2400 g/mm holographic grating. For this analysis, an aliquot of the nanoparticle in hexane was dried and subsequently dissolved in warm (~75° C) aqua regia for 30 min to ensure complete dissolution of metal into the acid. The solution was then diluted with 2% HN0₃ solution for analysis. ¹H-NMR and ¹³C-NMR spectra were recorded on a Bruker Avance DPX 400 MHz spectrometer.

[0063] Other methods of nanoparticle characterization are known to those of ordinary skill in the catalytic art.

Preferred embodiments

[0064] To demonstrate that ammonia borane is the source of hydrogen in the reactions, and not isopropanol, the inventors performed the hydrodechlorination of dichlorobenzene in 10% aqueous isopropanol without adding ammonia borane and found the yield of dechlorinated products to be less than 3%. The inventors also tested the reaction in aqueous ammonia borane solution without adding isopropanol as a co-solvent, and obtained a 76% yield of benzene. The reduction in yield from 99% (10% aqueous isopropanol solvent) to 76% (pure water as the solvent) is likely caused by the poor solubility of dichlorobenzene in pure water. When 10% isopropanol was added to improve the dichlorobenzene solubility, the reaction was completed within 5 hours and all the dichlorobenzene was converted to benzene. Ammonia borane is both the hydrogen source, and as a base to neutralize the hydrochloric acid generated during the reaction, which is key to maintaining the pH of the reaction mixture and to stabilizing the nickel/palladium/NG catalyst.

[0065] Using Ni₃oPd7o/ nitrogen-doped graphene as the catalyst, the inventors studied the time-dependent ammonia borane-initiated hydrodechlorination of chlorobenzene at 40°C. FIG. 2A shows the concentration changes of chlorobenzene and benzene over time in the presence of 3 mol% NiPd/NG. The disappearance of chlorobenzene and growth of benzene follows the exponential concentration changes of a first order reaction, indicating that the reaction proceeds without formation of other detectable intermediates. As shown in FIG. 4, the inventors examined a series of other mono- halogenated aromatic compounds using these reaction conditions. NiPd/NG is an efficient and selective hydrodechlorination catalyst for these substrates. Chlorobenzene, 2-chloronaphthylene and 3-chloropyridine are reduced in greater than 94% yield (entries 1-3). The reaction is effective for substrates with either electron-donating (entries 4-9, 13- 14) or electron-withdrawing groups (entries 10-12, 15). The conversion is not sensitive to the position of the halogen atom relative to other functional groups (entries 4-12).

Hydroxyl, amine, amide, and carboxylic acid groups are not reduced under the reaction conditions. Furthermore, the reaction can be extended to brominated substrates (entries 16-21).

[0066] Encouraged by the general applicability of NiPd/NG to monohalogenated substrates, the inventors extended the study to substrates containing multiple chlorine or bromine atoms. Using 1 ,2-dicholorobenzene as an example, the inventors examined the time-dependent hydrodechlorination at 50°C. As shown in FIG. 2B, the first hour of the reaction gives exponential decay of dichlorobenzene accompanied by an increase in both the chlorobenzene and benzene concentrations. This pattern is typical of a stepwise process in which the two chlorine atoms are reduced sequentially. The

chlorobenzene concentration reaches a maximum at 2 hours, and subsequently decreases with a corresponding increase in the concentration of the benzene final product. The reaction is complete after approximately 5 hours. During the course of the reaction, the inventors did not detect any other intermediates by gas chromatography- mass spectroscopy (GC-MS).

[0067] As shown in FIG. 5, the inventors examined other polyhalogenated substrates using these reaction conditions. Dichlorinated substrates (entries 1-6) are dehalogenated to their parent compounds in high yield. The environmental pollutants 2,4- dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid and 2, 3,7,8- tetrachlorodibenzodioxin (entries 7-9) are all completely dechlorinated in high yield under the reaction conditions. The inventors also examined five chlorinated biphenyl substrates (entries 10-14). Compounds 10-12 that contain chlorine atoms m eta and/or para to the biphenyl bond are fully reduced under the standard conditions. In contrast, substrates with chlorine atoms ortho to the biphenyl bond are reduced more slowly (entries 13 and 14). These are the most sterically hindered positions in the molecule, and the ortho chlorine substituents enforce a perpendicular geometry of the two phenyl rings. These substrates require 12 hours to achieve complete reduction of all of the C-CI bonds. In a similar manner, the four bromine atoms in PEDE (entry 12) that are ortho to the ether oxygen reside in sterically hindered positions, and PEDE also requires 12 hours for full dehalogenation.

[0068] The catalytic material of the invention can be recycled through several sequential hydrodehalogenation reactions. The inventors measured the stability of the catalyst by observing nickel/palladium nanoparticle morphology and composition changes before and after the hydrodechlorination of dichlorobenzene. After the first reaction was complete, the inventors separated the catalyst from the reaction solution by filtration, and washed the catalyst with water and isopropanol. The inventors then re-used the catalyst in the next hydrodehalogenation reaction. The analyses provided in FIG. 8 show that after the 5^th reaction/separation cycle, the catalyst had no obvious loss in activity and the product yield remained >91 %.

[0069] Transmission electron microcopy, as shown in FIG. 9, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses of the catalyst after the 5th reaction cycle showed that the nanoparticles display no obvious morphology changes or aggregation. The nanoparticle composition is stabilized at Ni₂₈Pd₇₂. These analyses show that nitrogen-doped graphene provides the necessary anchoring sites to stabilize nickel/palladium nanoparticles against aggregation. The combination of nitrogen-doped graphene and ammonia borane neutralizes the hydrochloric acid generated during the reaction, and prevents nickel from leaching out of the nickel/palladium nanoparticles.

[0070] The following Example is provided to illustrate the invention, and should not be considered to limit its scope in any way.

EXAMPLE

Characterization data of products

[0071] Phenol. ¹H-NMR (400 MHz, CDC ): 6 7.36 (t, J = 7.4 Hz, 2H), 7.08 (t, J = 7.4 Hz, 1 H), 6.99 (d, J = 8.0 Hz, 2H), 6.514 (bs, 1 H); ¹³C-NMR (100 MHz, CDCI₃): <5 155.1 ,

130.0, 121 .3, 1 15.6.

[0072] Anisole. ¹H-NMR (400 MHz, CDCI₃): 6 7.38 (t, J = 7.4 Hz, 2H), 7.06-6.99 (m, 3H), 3.88 (s, 3H); ¹³C-NMR (100 MHz, CDCb): J 159.6, 129.5, 120.7, 1 14.0, 55.2. [0073] Benzoic acid. ¹ H-NMR (400 MHz, CDCI₃): 6 13.10 (bs, 1 H), 8.19 (d, J = 7.6 Hz, 2H), 7.66 (t, J = 7.4 Hz, 1 H), 7.52 (t, J = 7.2 Hz, 2H); ^{1 3}C-NMR (100 MHz, CDCI3): d

172.8, 133.9, 130.2, 129.4, 128.5

[0074] Aniline. ¹³C-NMR (100 MHz, CDCI3): d 172.8, 133.9, 130.2, ¹H-NMR (400 MHz, CDCI3): J 7.28 (t, J = 7.4 Hz, 2H), 6.89 (t, J = 7.4 Hz, 1 H), 6.77 (t, J = 7.6 Hz, 2H), 3.70 (bs, 2H); ¹³C-NMR (100 MHz, CDCI3): <5 146.6, 129.4, 1 18.6, 1 15.24.

[0075] 2-phenoxyacetic acid. ¹ H-NMR (400 MHz, CDCI3): d 1 1 .67 (bs, 1 H), 7.35 (t, J = 7.2 Hz, 2H), 7.06 (t, J = 7.2 Hz, 1 H), 6.96 (d, J = 7.6 Hz, 2H), 4.72 (s, 2H); ¹³C-NMR (100 MHz, CDCI3): d 175.1 , 157.4, 129.7, 122.2, 1 14.7, 64.8. HRMS calculated for C₅H₅0₃ (M- Hr 151 .0393, found 151 .0395. This compound has been reported previously by Discekici et ai., Chem. Commun. 51 , 1 1705-1 1708 (2015)).

[0076] 4-chloro-1.1 '-biohenyl. ¹H-NMR (400 MHz, CDCI3): <5 7.62-7.56 (m, 4H), 7.52-7.40 (m, 5H); ¹³C-NMR (100 MHz, CDCI3): <5 140.0, 139.7, 133.4, 129.0, 128.9, 128.5, 127.7, 127.0. GC-MS calculated for C^HgCI (M)⁺ 188.04, found 188.0. This compound has been reported previously by Salemi et ai., Rsc. Adv. 6, 52656-52664 (2016)).

[0077] 3.4.4 '-thchloro- 1.1 '-biphen yl. ¹H-NMR (400 MHz, CDCI3): 6 7.65 (s, 1 H), 7.53- 7.43 (m, 5H), 7.39 (d, J = 8.4 Hz, 1 H), 7.57-7.53 (m, 1 H); ¹³C-NMR (100 MHz, CDCI3): <5 140.0, 137.2, 134.4, 133.0, 131.8, 130.8, 129.2, 128.8, 128.2, 126.2. GC-MS calculated for C12H9CI (M)⁺ 255.96, found 256.0. This compound has been reported previously by Zhou et ai., Angew. Chem. Int. Edit. 53, 3475-3479 (2014)).

[0078] 3.3'.4.4'-tetrachloro- 1.1 '-biphenyl. H-NMR (400 MHz, CDCI3): <5 7.62 (d, J = 8.0 Hz, 2H), 7.53-7.35 (m, 4H); 13MR (100 MHz, CDCI3): <5 138.7, 133.5, 132.8, 131.5,

128.9, 126.4. GC-MS calculated for C12H6C14 (M)⁺ 289.92, found 290.0. This compound has been reported previously by Er et ai., Eur. J. Inorg. Chem. 1729-1738 (2009)).

[0079] 2.2'.6.6'-tetrachloro- 1.1 '-biphen yl. ¹ H-NMR (400 MHz, CDCI3): 6 7.45 (d, J = 8.0 Hz, 4H), 7.34 (d, J = 8.0 Hz, 2H); ¹³C-NMR (100 MHz, CDCI3): 6 135.5, 135.4, 130.5, 128.5. GC-MS calculated for C12H6CI14 (M)⁺ 289.92, found 290.0. This compound has been reported previously by Praz et ai., Chem. Commun. 51 , 16912-16915 (2015)).

OTHER EMBODIMENTS

[0080] The contents of all references cited herein are incorporated by reference in their entireties.

[0081] Having thus described in detail preferred embodiments of the present invention, other embodiments will be evident to those of ordinary skill in the catalytic art. It should be understood that the foregoing detailed description is provided for clarity only and is merely exemplary. The spirit and scope of the present invention are not limited to the above examples, but are encompassed by the following claims.

Claims

CLAIMS We claim:

1. A catalytic material for catalyzing a desired chemical change, conversion or synthesis,

wherein the catalytic material comprises monodisperse nickel palladium (NiPd) alloy nanoparticles supported on nitrogen-doped graphene, wherein the nanoparticles are formed by co-reduction of nickel and palladium, which catalytic material is effective to catalyze a tandem reaction that:

(a) converts a halogenated arene compound to an unhalogenated arene compound; and

(b) oxygenates a nitrogen-containing hydrogen source.

2. The catalytic material of claim 1 , wherein the hydrogen source is or includes ammonia borane.

3. The catalytic material of claim 1 , wherein the nanoparticles are grown as

polycrystalline solid solution or alloy nanoparticles having a particle size between 2 and 4 nm.

4. The catalytic material of claim 1 , wherein the nanoparticles are grown as

polycrystalline solid solution or alloy nanoparticles having a particle size about 3 nm in length

5. The catalytic material of claim 1 , wherein the halogenated arene compound is selected form the group consisting of dioxin, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and the components of Agent Orange.

6. The catalytic material of claim 1 , wherein the catalytic material is recoverable and reusable multiple times without loss of catalytic activity.

7. The catalytic material of claim 1 , wherein the catalytic material is recovered and reused multiple times without loss of catalytic activity.

8. The catalytic material of claim 1 , for use in environmental remediation.

9. The catalytic material of claim 1 , for use in producing a pharmaceutical compound or a pharmaceutical intermediate.

10. The catalytic material of claim 1 , wherein nanoparticles are recoverable and reusable multiple times without loss of catalytic activity.

1 1. The catalytic material of claim 1 , wherein nanoparticles are recovered and reused multiple times without loss of catalytic activity.

12. The catalytic material of claim 1 , wherein the catalytic material converts a

chlorinated arene compound to a chlorinated arene compound.

13. The catalytic material of claim 1 , wherein the catalytic material has a Ni₃oPd₇o, N oPdeo or other palladium-rich polycrystalline structure.

13. The catalytic material of claim 1 , wherein the catalytic material has a Ni₃oPd₇o polycrystalline structure.

14. A process for making a catalytic material, the process comprising the steps of forming polycrystalline nickel/palladium alloy nanoparticles, and assembling the nanoparticles on a nitrogen-doped graphene support.

15. A catalytic material made by the process of claim 10.

16. A method of environmental remediation, comprising the step of:

contacting a catalytic material comprising palladium-rich nickel palladium (NiPd) alloy nanoparticles supported on nitrogen-doped graphene, which catalytic material catalyzes a tandem reaction that

(b) hydrogenates a second nitrogen-containing feedstock or group to primary amine;

wherein the catalysis results in the dehalogenation of environmental

unhalogenated arene compounds.